Many integrated circuits, such as display drivers, require a combination of high-voltage driving capability (an output voltage swing up to 100V or more) and a digital control using standard 5V CMOS logic. Hence, complex level-shifting circuits are needed to convert the 5V control signals into the desired high-voltage output waveforms. Moreover, in many of those applications, the system is battery-powered and very severe constraints are put on the power consumption of the level-shifters. One application where both high-voltage driving capability and low power consumption are required in the design of driver chips is in automotive applications.
Level shifters, in general, are utilized in a circuit to transition from a low voltage signal to a high voltage signal. In the alternative, a level shifter may be used to transition from a high voltage signal to a low voltage signal. Level shifters are commonly used for multi-rail or multi-power supply designs, where multiple rails or multiple power supplies exist and numerous signals reference these multiple rails or power supplies. These signals interact with various logic blocks that operate on different power supplies. Thus, every time a high voltage signal is transferred to a low voltage block, the signal must be level-shifted. Similarly, in the alternative, when a low-voltage signal is transferred to a high voltage block, the signal must be level-shifted.
Most of the circuits in the automotive electronic systems are high voltage circuits. High voltage level shifters, however, are large. In addition, when there are a lot of signals that need to be level-shifted, it becomes very difficult to incorporate large level shifters in a system's design. Thus, to date, there has been no way of designing around the affects of incorporating high voltage level shifters in a system. In particular, high-voltage signals in a electronic system leads to high-voltage components which are larger than low-voltage components. Secondly, another deficiency of high-voltage level-shifters is that they are slow. Primarily, because the high-voltage components are large, these components cannot be switched as fast as low-voltage components.
Referring to known a high-voltage level-shifter 10 as is displayed FIG. 1, a low-voltage input signal IN1 is level-shifted to an high voltage output signal Out1. Transistors, MN1 and MN2, provide the level shifting function to shift a voltage applied at the input signal node IN1 to a signal at the output node Out1. Transistors, MP1 and MP2, protect the drain-to-source voltage Vds and gate-to-source voltage Vgs of transistors, MP4 and MP3. Diodes, D2 and D1, only provide protection for the gate-to-source voltage Vgs of transistors, MP2 and MP1. A high voltage reference HVref1 is applied to gate of transistors, MP2 and MP1, such that the source of each transistor, MP2 and MP1, will not go one gate-to-source voltage Vgs above the HVref1 signal. This design for a high voltage level-shifter is troublesome in that it requires a large and complex circuit to provide a high voltage reference HVref1.
FIG. 2 shows the another known level-shifter 20 that is self-biased, wherein a low-voltage input signal IN2 is level shifted to an high voltage output signal Out2. Transistors, MN3 and MN4, are switched on and off to provide the level-shifting feature of level-shifter 20. Transistors, MP6 and MP5, protect the drain-to-source voltage Vds and gate-to-source voltage Vgs of transistors, MP8 and MP7. As shown, a current source I1 is pulled through two reverse bias Zener diodes, D4 and D3, which have a 6.5V breakdown voltage for this particular technology. Those skilled in the art would recognize that even if a Zener diode has a 13V breakdown voltage, the only requirement is that the breakdown voltages of diodes, D4 and D3, must correspond with the vgs of transistors, MP5 and MP6. Diodes, D4 and D3, provide the high voltage reference signal which is applied to each gate of transistors, MP5 and MP6, such that the source of each transistor, MP5 and MP6, will not go one gate-to-source voltage Vgs above the high voltage reference signal.
The difference between the design of high voltage level-shifter 20 and the design of the level-shifter 10 in FIG. 1 is the way in which the high voltage reference signal HVref1 is generated. This approach, however, requires the external current source I1.
Thus, there exists a need for a self-biased high voltage level shifter that provides level shifting a low voltage signal (<5V) to a high voltage signal (˜40V), with no static power dissipation while still protecting all devices. Furthermore, there exists a need for a simple, yet, cost-effective design that does not require an external current source.
The present invention is directed to overcoming, or at least reducing the effects of one or more of the problems set forth above.